1. Field of the Invention
The present invention relates to an improvement in a low pressure discharge lamp having a discharge tube containing therein mercury and a rare gas, and requiring only about half as much commercial power source voltage being supplied to said discharge tube by using a stabilizer.
2. Description of the Prior Art
Generally speaking, argon gas as a rare gas is contained in a fluorescent discharge tube of a low pressure discharge lamp, such as fluorescent lamp. However, recently a new type of a low pressure discharge lamp having a discharge tube of smaller diameter containing therein mercury and a rare gas such as krypton or xenon, which has heavier atomic weight than argon, is proposed. In such discharge tube an energy loss which is caused by elastic collisions of atoms is reduced by enclosing the rare gas into the discharge tube. Since the rare gases of heavy atomic weight have a lower ionization potential, the mobility of a charged particle in the discharge tube is reduced. Accordingly, the cathode drop is reduced and efficiency of the lamp is improved. However, in the above-mentioned sort of fluorescent lamp, a flickering phenomena remarkably appears under the condition of a low ambient temperature, and as a result the lamp beam becomes low, and further more the stabilizer loss increases by an increasing of the load current.
The flickering phenomena is produced by a moving striation which is peculiar to rare gas discharge in the positive column, and the more heavy the atomic weight is, the more it appears to a higher temperature. The reason is assumed as follows: As the ambient temperature of the discharge tube drops, the mercury vapor pressure exponentially drops, and hence the majority of ions in the discharge tube gradually change from mercury ions to rare gas ions, and accordingly the moving striation caused by the rare gas discharge appears. However, when krypton (ionization potential is 13.99 V), which has the atomic weight heavier than argon (ionization potential is 15.76 V), is sealed in the discharge tube as the rare gas, because of its small ionization potential against mercury's (ionization potential is 10.43 V) the majority ions in the discharge tube gradually change from mercury ions to rare gas ions, even under the condition of a comparative high temperature where a small amount of mercury ions still remain in the discharge tube. In case that the rare gas sealed in the discharge tube is a mixing gas consisting of various rare gasses, the flickering phenomena is effected by the heaviest rare gas of the component gas. And hence the more the mixing ratio of the gas is the more prominent the flickering phenomena caused by the moving striation of the rare gas discharge appears under the condition of a comparatively high temperature.